The GetInitializer method allows retrieving an Action that holds all the registered initializers for a certain type T. This method is useful for extension scenarios. The SimpleInjector.Extensions project is probably the biggest user of this feature.
 
This feature however, is not useful for normal use, but it does pollute the main API. Not only this, since the first 5 characters are the same as that of "GetInstance" (which will mostly be used), it's easy to pick the wrong method while working with IntelliSense.
 
Instead, this method can be made internal and functionality can be made accessible through an extension method in a sub namespace (SimpleInjector.Advanced for instance).
 
Removing this method from the Container is a breaking change!